1. Field of the Invention
The invention relates generally to piezoelectric microactuators for data recording disk drives with dual-stage actuators, and more particularly to moving-slider type piezoelectric microactuators.
2. Description of the Related Art
Data recording disk drives, such as magnetic recording disk drives, store information in data tracks on the data surface of a rotatable magnetic recording disk. A read/write head or transducer that reads data from and writes data to the data surface is located on an air-bearing slider that is supported by a cushion of air on the rotating disk. The slider is attached to a flexible suspension at the end of a rigid arm and is moved generally radially from track to track by an actuator. The disk drive actuator is typically a rotary voice coil motor (VCM) that moves the actuator arm and the attached suspension and slider generally radially to position the head at the desired track under the control of a servo control system that receives pre-recorded servo position information from the data surface. As the data tracks on the disk are made narrower and placed closer together to increase the data density, it becomes increasingly difficult for the actuator and the servo control system to quickly and accurately position the head over the desired track and to provide track following. For example, a servo control system with a VCM actuator will have difficulty achieving a servo loop bandwidth greater than 2 kHz.
One way to improve the servo bandwidth is with a dual-stage actuator, where a VCM actuator is a first stage that provides coarse positioning of the head and a secondary actuator is a second stage that provides fine positioning of the head. The secondary actuator can be a moving-slider type of actuator that is located between the end of the suspension and the slider and moves the slider relative to the suspension. One such moving-slider type of secondary actuator is a rotary electrostatic microactuator (so called because it is a micro-electromechanical system (MEMS) device), as described in U.S. Pat. Nos. 5,959,808 and 5,995,334. Advances in integrated circuit technology in recent years have led to the development of MEMS devices of micrometer dimensions that can be actuated and controlled using electrostatic and other methods, such as mechanical, electromagnetic, fluidic and thermal. MEMS manufacturing technologies are a combination of the more established semiconductor micro-fabrication techniques with newer developments in micromachining.
Because the moving-slider microactuator is electrostaticly driven it generally applies a relatively small force to provide a relatively large displacement of the slider, and thus typically uses relatively soft springs to support the movable slider. However, in some disk drive applications the external disturbance forces, such as may occur from air flow and head-disk contact, can be relatively large, which results in an increased level of head position error.
Moving-slider microactuators that use piezoelectric drivers have been proposed. These microactuators typically require the piezoelectric element to be located near the end of the slider that supports the head, such that a large external force can damage the piezoelectric element. Also, these microactuators typically move the slider in translation, i.e. in a linear direction, such that the counter-force can excite the natural vibration modes of the suspension, which limits the achievable servo bandwidth of the dual-stage actuator. Because piezoelectric microactuators also require a larger force but provide less displacement than comparable electrostatic microactuators, they may not provide adequate displacement to maintain the head centered on the data track. U.S. Pat. No. 6,381,104 shows a piezoelectric moving-slider microactuator that moves the slider by rotation, but the rotatable portion is not supported at its axis of rotation, there are no torsional springs to assure pure rotary motion, the displacement of the head is generally the same as the displacement of the piezoelectric element, and the piezoelectric elements are located near the end of the slider that is most likely to contact the disk.
What is needed is a piezoelectric moving-slider rotary microactuator as the secondary actuator for a dual-stage-actuator disk drive that is substantially resistant to external forces, provides substantially pure rotary motion, and amplifies the displacement of the piezoelectric driver.